Not applicable.
This invention relates generally to vehicle radar systems and more particularly to a radar system to detect other vehicles and objects in close proximity to the vehicle.
As is known in the art, radar systems have been developed for various applications associated with vehicles, such as automobiles and boats. A radar system mounted on a vehicle detects the presence of objects including other vehicles in proximity to the vehicle. In an automotive application, such a radar system can be used in conjunction with the braking system to provide active collision avoidance or in conjunction with the automobile cruise control system to provide intelligent speed and traffic spacing control. In a further automotive application, the radar system provides a passive indication of obstacles to the driver on a display.
A continuing safety concern in the operation of automobiles is the difficulty in seeing objects in the side blind spots of the automobile. Accidents often occur when an automobile impacts another vehicle in its blind spot when changing lanes.
Rear and side view mirrors of various sizes and features are typically used in an effort to improve visualization of blind spots. For example, convex mirrors provide a larger view than flat mirrors. However, objects viewed in a convex mirror appear farther away than their actual distance from the vehicle. Also, the view through mirrors degrades during conditions of rain, snow, or darkness.
There is a need for an effective way to detect obstacles in a vehicle""s blind spots, and generally in close proximity to the vehicle, which is accurate and reliable during all types of environmental conditions including rain, snow, and darkness. A further characteristic of an effective detection system is a well-defined detection zone within which there is a very high probability of detection, and outside of which there is a very low probability of detection.
A method for detecting an object with a radar system includes transmitting a transmit signal, receiving a receive signal generated by at least a portion of the transmit signal impinging on the object, calculating a difference signal in response to the transmit signal and the receive signal, performing an FFT on the difference signal to provide an FFT output signal, computing a derivative of the FFT output signal, and detecting the object in response to a zero crossing of the derivative of the FFT output signal. The range to the object is determined by the frequency at which the zero crossing of the FFT output signal occurs. In one embodiment, the derivative is a second derivative.
Also described is a method for detecting an object with a radar system which includes generating a detection table containing a plurality of indicators, each of which is indicative of the presence or absence of an object in proximity to the radar system. Each indicator is associated with a respective radar beam and processing cycle. The method further includes combining at least two of the indicators, and providing an object detection if at least one of the combined indicators indicates the presence of the object. In the illustrated embodiment, combined indicators are associated with different radar beams and/or different processing cycles.
With this arrangement, objects in proximity to the radar system are detected with high probability, and the range to the detected objects is determined with high accuracy. By using the detection table, the method provides a reduction in the probability of a false detection. Use of the derivative of the FFT output signal, and in particular the second derivative, permits detection of certain objects which might otherwise go undetected.
Radar apparatus for detecting an object includes a transmitter for generating a transmit signal, a receiver for receiving a receive signal generated by at least a portion of the transmit signal impinging the object, a differencing circuit for calculating a difference signal in response to the transmit signal and the receive signal, an FFT processor for performing an FFT on the difference signal to provide an FFT output signal, a derivative processor for computing a derivative of the FFT output signal, and a detector for detecting the object in response to a zero crossing of the derivative of the FFT output signal. The detector is further capable of determining the range to the object in response to the frequency at which the zero crossing of the derivative occurs.
The radar apparatus includes a memory in which is stored a detection table containing a plurality of indicators, each indicative of the presence or absence of the object. A processor is provided for combining at least two of the indicators in the detection table, and providing an object detection message if at least one of the combined indicators is indicative of the presence of the object.
The radar apparatus, like the detection techniques, provides reliable detection of objects in proximity to the radar system with high probability, and determines the range to the object with high accuracy.